Radio telegraph reception



' Aha Sept. 19, 1944.

RADIO TELEGRAPH. RECEPTION Filed Aug. 13, 1941 2 Sheets-Sheet 1 #1 a Qll 5 ai ca I INVENTOR I BY 07462.53 4 5409 A TT ORNE Y c. w. EARP 2,358,448

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Sept. 19, 1944. w, EARP f 2,358,448

RADIO TELEGRAPH RECEPTION Filed Aug. 13, 1941 2 Sheets-Sheet 2 IFS Has,

IN VEN TOR BY 7 gy ATTORNEY Patented Sept. 19, 1944 UNITED STATE .2,ss,44 s v mnno TELEGRAPH RECEPTION i Charles 'W. Earp,

Application August 13,

London, England, assig nor to International Stand ard Electric Corporation, New York, N. Y., a corporation of Delaware 1941, Serial No.40s,64.2

In Great Britain September 28, 1940 9 Claims. l Cl. 250-8) -The present invention relates to radio telegraph systems and receivers for use therein. One object of the invention is to guard against disturbance of the telegraph signals.

According to the invention, there nals are radiated by intermittent interruption of a radio frequency wave modulated by a low frequency tone, the receiving apparatus being so arranged that it assumes the same predetermined condition when the transmission is disturbed, whether by interference or by fading.

. Also according to the invention, there is prois provided ai radio telegraph system in which telegraph sigvided a radio telegraph receiving arrangement for receiving telegraph signals which are radiated simultaneously. on a plurality of different radio frequency waves, the'receiving apparatus being so arranged that it assumes the same peredetermined condition when the transmission is disturbed, whether by interference or by fading.

Embodimentsof radio telegraph receiving arrangements according to the invention will now be described with reference to the accompanying drawings comprising Figs. l-5.

Fig. 1 is a block schematic of aradio telegraph receiver according to the invention;

Fig. 2 is a circuit diagramof a thermionic valve circuit suitable for use as the unit CO in the arrangement of Fig. l;

Figs. 3, 4' and 5 are modifications of Fig. 2.

The arrangement of Fig. 1 is a modification of the arrangement of Fig. l of my prior British patent specificationNo. 540,839, acceptedOct. 31,

ahead modulator, when no carrier, but two equal sidebands would be radiated; this has the ad.-

vantagethat all the componentwaves have the same amplitude, so that similar receiving channels may be used for each wave.

An analogous three frequency transmission may be effected by the keying of a partially balanced modulator, whereby three frequencies of equal amplitude may be produced. 1

The interrupted signals of all the frequencies are received on antenna AM of the receiver of Fig. 1. These signals are amplified in an amplifier Al the output of which is passed through a frequency changer comprising a detector DI and oscillator OI. The. resultant intermediate fre-v quencies are then amplified in A2. 1 The Output of A2 is applied to a second detector D2 where the frequencies are again reduced by 'action'of 1941, and the description given herein will therefore berestricted 'to a brief description of the prior arrangement and a more particular description of the changes which have been made therein. The prior arrangement was for receiving transmissions of the kind in which a telegraph channel is produced by the keying of a radio frequency wave which is then radiated from the antenna of a radio transmitter. In order to provide greater freedom from th disturbance of the radio telegraph si als due to fadingand due to interfering signals from other transmitters, it is now proposed to radiate the same signal simultaneously on a plurality of different radio frequency waves.

Transmission may conveniently be effected by intermittently interrupting a radio frequency wave which has been modulated by a low frequency tone; in this case the telegraph signals are radiated on three frequencies, viz. on a carrier and two sidebands. Another, suitable transmission would be thekeyed output from a balseparate signal paths'SP, SP,

oscillator 02 to values which may be more easily separated by selector filters F, F and? to apply the signals of different signal frequencies to SP", the outputs of these paths being applied to a conversion circuit CC to be described in more detail later. The output of CC is applied to the telegraph relay circuit RC which repeats the marking and spacing telegraph impulses. The signals are applied over security apparatus SA, which serves torepeat' the signals back to the transmitter, to teleprinter recorder TP.

A second output of detector D2 is connected over band pass filter Fl which will pass all the signal frequencies, as well. as interference voltages, and amplifier A3' to detector D 31. f The outputof D3 is appliedover interference path I1 to a second input of converter CC, a low pass filter F2 being used if required.

The most obvious method of applying these outputs to the circuit CC would be t combine them and to apply the combined output to the input of a simple valve circuit. This method, however, would have the serious disadvantage that the interference components in all the si nal paths would add up to produce a voltage which would be much greater than when receiving on a single frequency. The interference filter F2 would consequently have'to be increased in band width, ,or alternatively the noise level in this filter would have to be raised by increasing the gain of the amplifier A3. This would result in the disturbing effect of interference being seriously increased, for during selective fading affectsignal strength would be reduced whereas the inthe difference frequencies.

terference voltage applied over the interference path IP would remain substantially unchanged. Fig. 2 shows a modified arrangement of the conversion circuit CC which overcomes this difficulty by arranging that the signal paths SP, SP, SP" operate into individual rectifiers RS, RS, RS" which operate into a common load circuit.

Using the circuit-of Fig. 2, the rectified voltage delivered to the grid. of. valve V3 corresponds to the strongest of the three received signals. If the output on SP is the strongest signal, for ex-' ample, the grid of V3 becomes biased negatively by the operation of rectifier RS. Therectified voltage set up across the grid resistance R1 automatically biases the so that the smaller outputs on SP not operative. If only interference is present on the channels SP, rectified voltage applied to V3 over interference path IP is substantially the same as the peak rectified voltage that would. be applied thereto due to the interference on V since R8 carries large rectified current; tubeV4 is biased to cut-off and no marking signals are repeated into RC. This arrangement also avoids the disadvantage that if the different frequencies wereadded. together before recti fication signal envelopes would be produced at Fig. 3 is a modification of Fig. ZQdispen sing with the valve V3. In this case the'rectifiers RS,- RS', RSf'are' connected in the opposite sense to their connections in Fig. 3 so their outputs tendtodrive the grid of V4 positively. The out put from Rl' tendsto drive the grid of V4 negatlvely' so that the voltage actually applied to the grid of V4-is the difference between the voltages set up across R1 and R8.

Figl 4is" a modified circuit designed to give a high freedom from interfering signals; Each signal" p'athSPlSP, SP" has its own rectifier RS;'RS', RS; and each rectifier its own load resistor R1, RT, R"1, and each' load has, associated with it, a separate valve V3, V3',.V3". In order that jamark signal'can be sent to the relay circuit RC, signals must be" present on all the signal paths. so that all the valves V3, V'3, V"3 are drivento cut-off. If there is no signal on anygoneof the signal paths, then the associated valve will draw anode current and bias the valve V4, thus preventing the relay circuit RC taking up the mark condition, It will be seen, therefore, that a false mark cannot be produced by in teference unless it is present on all signal paths, and absent from the interference path;

Fig.5 showsa further modification in which a separate interference path is provided for each signal path. 'The separate interference paths IP, IP', IP"- areconnected through separate rectifiers RI, RI, RI" to a common load circuit 03, Rflwhi'chthusreceives a voltage proportional to themaximum interference on any of the channels IP, IP, IP". This provides protection againstfalse markingby interference which happensto be presenton all signal paths at once, for interference which is present on all signal paths is highly likely, to be present on at least one interference path. If so, then a false mark is prevented. It should be noted that the use of sev eral interference paths does not affect the overall signal-to-noise ratio for normal types of noise which are uniformly distributed throughout the frequency bands used.

' 1. A radio telegraph receiving arrangement rectifiers RS and-RS and SP" are SP, SP", then the peak a single channel.

comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said last named means comprising telegraph relay apparatus arranged to assume a marking condition in response to a marking signal being received over li'i any one of said radio frequency waves. r

2..A 'radio telegrpah receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said last named means comprising telegraph relay apparatus arranged to assume a marking condition only when a marking signal is received over all of said radio frequency waves in the ab} sence of any substantial interference.

3. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio'freq'uencies, a receiver amplifier, selectivemeans; selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive-to'either interference disturbances or fading of'said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents. corresponding to said different frequency waves, and separate signal paths coupled to said signalfilters, said control means including a further-filter to select interference waves and applythem to an interference path. v

4. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative ofsaid different radio frequencies to said receiver amplifier, and control means. in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicativeof the interference, said selective means comprising signal filters to select signal currents corresponding to said different frequency waves, separate signal paths coupled to said signal filters, a further filter to select interference waves and apply them to an interference path, and individual rectifiers which have their output circuits connected in parallel coupled to the outputs of said signal filters.

5. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals. rep resentative of saiddiiferent radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents corresponding to said different frequency waves, separate signal paths coupled to said signal filters, a further filter to select interference waves and apply them to an interference path, and a resistance capacity circuit connected to automatically bias all of said rectifiers to an extent which is proportional to the greatest of the outputs applied to said rectifiers.

6. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents corresponding to said different frequency waves, separate signal paths coupled to said signal filters, a further filter to select interference waves and apply them to an interference path, and individual rectifiers which have their output circuits connected in parallel coupled to the outputs of said signal filters, and an individual rectifier in the output of said further filter which has its output circuit so connected that the voltage produced therein has an opposing effect to that produced by that of the signal rectifiers.

'7. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents corresponding to said different frequency waves, separate signal paths coupled to said signal filters, a further filter to select interference waves and apply 8. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier, selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents corresponding to said different frequency waves, separate signal paths coupled to said signal filters, a further filter to select interference waves and apply them to an interference path, and individual rectifiers which have their output circuits connected in parallel coupled to the outputs of said signal filters, and an individual rectifier in the output of' said further filter, a valve, the outputs from all of said rectifiers being applied to the grid of said valve, the interference rectifier being connected in the opposite sense to the signal rectifiers.

9. A radio telegraph receiving arrangement comprising means for simultaneously receiving signals radiated simultaneously on a plurality of different radio frequencies, a receiver amplifier,

selective means selectively applying signals representative of said different radio frequencies to said receiver amplifier, and control means in said receiver responsive to either interference disturbances or fading of said signals to cause said receiver amplifier to assume a common predetermined condition indicative of the interference, said selective means comprising separate signal filters to select signal currents corresponding to said different frequency waves, separate signal paths connected to said signal filters, and a like number of separate interference filters to select interference currents and apply said selected interference currents to separate interference paths.

CHARLES W. EARP. 

